From be99ca2716972a712cde46092c54dee5e6192bf8 Mon Sep 17 00:00:00 2001 From: Wengang Wang Date: Thu, 13 Jun 2019 15:56:01 -0700 Subject: [PATCH] fs/ocfs2: fix race in ocfs2_dentry_attach_lock() ocfs2_dentry_attach_lock() can be executed in parallel threads against the same dentry. Make that race safe. The race is like this: thread A thread B (A1) enter ocfs2_dentry_attach_lock, seeing dentry->d_fsdata is NULL, and no alias found by ocfs2_find_local_alias, so kmalloc a new ocfs2_dentry_lock structure to local variable "dl", dl1 ..... (B1) enter ocfs2_dentry_attach_lock, seeing dentry->d_fsdata is NULL, and no alias found by ocfs2_find_local_alias so kmalloc a new ocfs2_dentry_lock structure to local variable "dl", dl2. ...... (A2) set dentry->d_fsdata with dl1, call ocfs2_dentry_lock() and increase dl1->dl_lockres.l_ro_holders to 1 on success. ...... (B2) set dentry->d_fsdata with dl2 call ocfs2_dentry_lock() and increase dl2->dl_lockres.l_ro_holders to 1 on success. ...... (A3) call ocfs2_dentry_unlock() and decrease dl2->dl_lockres.l_ro_holders to 0 on success. .... (B3) call ocfs2_dentry_unlock(), decreasing dl2->dl_lockres.l_ro_holders, but see it's zero now, panic Link: http://lkml.kernel.org/r/20190529174636.22364-1-wen.gang.wang@oracle.com Signed-off-by: Wengang Wang Reported-by: Daniel Sobe Tested-by: Daniel Sobe Reviewed-by: Changwei Ge Reviewed-by: Joseph Qi Cc: Mark Fasheh Cc: Joel Becker Cc: Junxiao Bi Cc: Gang He Cc: Jun Piao Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/ocfs2/dcache.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/fs/ocfs2/dcache.c b/fs/ocfs2/dcache.c index 2d016937fdda..42a61eecdacd 100644 --- a/fs/ocfs2/dcache.c +++ b/fs/ocfs2/dcache.c @@ -296,6 +296,18 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry, out_attach: spin_lock(&dentry_attach_lock); + if (unlikely(dentry->d_fsdata && !alias)) { + /* d_fsdata is set by a racing thread which is doing + * the same thing as this thread is doing. Leave the racing + * thread going ahead and we return here. + */ + spin_unlock(&dentry_attach_lock); + iput(dl->dl_inode); + ocfs2_lock_res_free(&dl->dl_lockres); + kfree(dl); + return 0; + } + dentry->d_fsdata = dl; dl->dl_count++; spin_unlock(&dentry_attach_lock);